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Abstract:

The present invention relates to a communication method of a base
station, which includes the base station including an indication of
whether the base station is a terminal acting as a base station or a base
station acting as a relay station in an SCD message or DCD message, and
transmitting the SCD message or the DCD message to a terminal.

Claims:

1. A communication method of a base station, comprising: the base station
including an indication of whether the base station is a terminal acting
as a base station or a base station acting as a relay station in a system
configuration descriptor (SCD) message or a downlink channel descriptor
(DCD) message; and the base station transmitting the SCD message or the
DCD message to a terminal.

2. A communication method of a relay station, comprising: the relay
station including an indication of whether the relay station is a
terminal acting as a relay station in an SCD message or a DCD message;
and the relay station transmitting the SCD message or the DCD message to
a terminal.

3. A communication method of a base station, comprising: the base station
including an indication of whether the base station is a multi-mode
apparatus in a neighbor advertisement (NBR-ADV) message; and the base
station transmitting the NBR-ADV message to a terminal.

4. The communication method of claim 3, wherein the indication includes
an indication of whether the base station is a terminal acting as a base
station or a base station acting as a relay station.

5. A communication method of a relay station, comprising: the relay
station including an indication of whether the relay station is a
multi-mode apparatus in an NBR-ADV message; and the relay station
transmitting the NBR-ADV message to a terminal.

6. The communication method of claim 5, wherein the indication includes
an indication of whether the relay station is a terminal acting as a
relay station.

7. A communication method of a base station, comprising: a first base
station currently providing a service to a terminal including information
about the terminal in a handover message (AAI-HO-CMD); and the first base
station transmitting the handover message to a second base station.

8. The communication method of claim 7, wherein the second base station
does not share the information about the terminal.

11. A communication method of a base station, comprising: a first base
station terminal providing a service to a terminal designating a first
path including the first base station as an active path; and the first
base station designating one or more paths including one or more second
base stations in a neighborhood of the first base station as an
alternative path.

12. The communication method of claim 11, wherein the first path is
changed to an alternative path, and one of the one or more second paths
is changed to an active path when a backhaul link of the first base
station is cut off.

13. A communication method of a base station, comprising: a first base
station transmitting information about a terminal provided with a service
from the first base station to a neighbor second base station; and the
first base station transmitting, to the terminal, information
representing that the information has been transmitted to the second base
station.

14. The communication method of claim 13, wherein the information
includes context information.

15. The communication method of claim 13, wherein the transmitting of the
information to the terminal comprises the first base station transmitting
a list of a plurality of second base stations to the terminal.

16. The communication method of claim 13, wherein the list of a plurality
of second base stations is aligned according to priority.

17. The communication method of claim 13, wherein the transmitting of the
information to the terminal comprises the first base station transmitting
priority of second base stations to the terminal.

18. A communication method of a terminal, comprising: the terminal
relaying a first base station providing a service to the terminal and a
second base station in a neighborhood of the first base station when a
relay link establishment between the first base station and the second
base station is unavailable; and managing a first path including the
first base station and a second path including the second base station as
an alternative path or an active path.

19. A communication method of a terminal using multiple carriers,
comprising: receiving carrier state information from a base station; and
the terminal changing a carrier according to the carrier state
information.

20. A communication method of a terminal using multiple frequencies,
comprising: receiving frequency state information from a base station;
and the terminal performing inter-frequency handover (inter-FA HO)
according to the frequency state information.

[0003] The present invention relates to a communication method of a base
station, a communication method of a relay station, and a communication
method of a terminal.

[0004] (b) Description of the Related Art

[0005] Disasters may destroy or damage important infrastructure. The
important Infrastructure includes various communication facilities such
as for wireless telephones, wired telephones, the internet, etc.
Destruction or damage to these communication facilities may increase
society congestion and make recovery of infrastructure difficult. In this
case, it is important to provide high reliability support such as means
for rapidly recovering or replacing the communication facilities. For
high reliability support, a mobile communication system (HR-Network)
needs to satisfy the following requirements.

[0006] First of all, backward compatibility with existing systems, that
is, Wireless MAN-OFDMA or Wireless MAN-Advanced Interface systems, must
be satisfied. Then, a base station (HR-base station, HR-BS), a terminal
(HR-mobile station, HR-MS) and a relay station (HR-relay station, HR-RS)
need to perform a multi-mode operation of functioning as other stations.

[0007] Furthermore, communication should be continued even when a base
station, a relay station, or a wireless link is unavailable, that is,
when a single point of failure (SPOF) is generated. In addition, direct
communication between different terminals must be performed. Multicast
transmission, that is, enhanced multicast communication, should be
available in a network, and path setup including multi-path management
for data transmission/reception and path management for managing
forwarding should also be available. However, conventional technologies
have only requirements, and thus a method for supporting multiple paths
is needed.

[0008] Particularly, path reestablishment is required when a relay station
or base station cannot properly perform the function thereof. If two or
more paths are established, it is possible to overcome re-routing delay
through an alternative path. However, when the alternative path is set
up, a network load may be generated and it is necessary to support
continuous establishment, maintenance, and change of the alternative
path.

[0009] When a base station provides a service through multi-carrier or
multi-frequency, if a certain carrier or frequency is not available for
the service or service quality is deteriorated, it is necessary to
overcome service quality deterioration through an alternative path.

[0010] Moreover, establishment of various paths may be performed when a
backhaul link is cut off and a base station operates in multiple modes
between base stations, between the base station and a relay station, or
between relays stations.

SUMMARY OF THE INVENTION

[0011] The present invention has been made in an effort to provide a
method for communication of a base station, a relay station, and a
terminal to continue providing a communication service through a neighbor
base station or a neighbor relay station when a base station or relay
station cannot perform the function thereof due to damage to a backhaul
link of the base station in a communication system.

[0012] The present invention provides a communication method by which a
base station providing a service using multi-carrier or multi-frequency
continues providing the service using another carrier or frequency. An
exemplary embodiment of the present invention provides a communication
method of a base station, including: the base station including an
indication of whether the base station is a terminal acting as a base
station or a base station acting as a relay station in a system
configuration descriptor (SCD) message or a downlink channel descriptor
(DCD) message; and the base station transmitting the SCD message or the
DCD message to a terminal.

[0013] Another exemplary embodiment of the present invention provides a
communication method of a relay station, including: the relay station
including an indication of whether the relay station is a terminal acting
as a relay station in an SCD message or a DCD message; and the relay
station transmitting the SCD message or the DCD message to a terminal.

[0014] Another exemplary embodiment of the present invention provides a
communication method of a base station, including: the base station
including an indication of whether the base station is a multi-mode
apparatus in a neighbor advertisement (NBR-ADV) message; and the base
station transmitting the NBR-ADV message to a terminal.

[0015] The indication may include an indication of whether the base
station is a terminal acting as a base station or a base station acting
as a relay station.

[0016] Another exemplary embodiment of the present invention provides a
communication method of a relay station, including: the relay station
including an indication of whether the relay station is a multi-mode
apparatus in an NBR-ADV message; and the relay station transmitting the
NBR-ADV message to a terminal.

[0017] The indication may include an indication of whether the relay
station is a terminal acting as a relay station.

[0018] Another exemplary embodiment of the present invention provides a
communication method of a base station, including: a first base station
currently providing a service to a terminal including information about
the terminal in a handover message (AAI-HO-CMD); and the first base
station transmitting the handover message to a second base station.

[0019] The second base station may not share the information about the
terminal.

[0020] Another exemplary embodiment of the present invention provides a
communication method of a base station, including: a first base station
terminal providing a service to a terminal designating a first path
including the first base station as an active path; and the first base
station designating one or more paths including one or more second base
stations in a neighborhood of the first base station as an alternative
path.

[0021] The first path may be changed to an alternative path, and one of
the one or more second paths may be changed to an active path when a
backhaul link of the first base station is cut off.

[0022] Another exemplary embodiment of the present invention provides a
communication method of a base station, including: a first base station
transmitting information about a terminal provided with a service from
the first base station to a neighbor second base station; and the first
base station transmitting, to the terminal, information representing that
the information has been transmitted to the second base station.

[0023] The information may include context information.

[0024] The transmitting of the information to the terminal may include the
first base station transmitting a list of a plurality of second base
stations to the terminal.

[0025] The list of a plurality of second base stations may be aligned
according to priority.

[0026] The transmitting of the information to the terminal may include the
first base station transmitting priority of the plurality of second base
stations to the terminal.

[0027] Another exemplary embodiment of the present invention provides a
communication method of a terminal, including: the terminal relaying a
first base station providing a service to the terminal and a second base
station in a neighborhood of the first base station when a relay link
establishment between the first base station and the second base station
is unavailable; and managing a first path including the first base
station and a second path including the second base station as an
alternative path or an active path.

[0028] Another exemplary embodiment of the present invention provides a
communication method of a terminal using multiple carriers, including:
receiving carrier state information from a base station; and the terminal
changing a carrier according to the carrier state information.

[0029] Another exemplary embodiment of the present invention provides a
communication method of a terminal using multiple frequencies, including:
receiving frequency state information from a base station; and the
terminal performing inter-frequency handover (inter-FA HO) according to
the frequency state information.

BRIEF DESCRIPTION OF THE DRAWINGS

[0030] FIG. 1 shows a communication state according to an exemplary
embodiment of the present invention;

[0031]FIG. 2 shows an example of establishment of a relay link by a base
station in case of backhaul damage according to an exemplary embodiment
of the present invention;

[0032]FIG. 3 shows an example of handover performed by a terminal in case
of backhaul damage according to another exemplary embodiment of the
present invention;

[0033]FIG. 4 shows an example of path reestablishment according to
another exemplary embodiment of the present invention;

[0034]FIG. 5 shows an example of path reestablishment according to
another exemplary embodiment of the present invention;

[0035]FIG. 6 shows an example of path reestablishment according to
another exemplary embodiment of the present invention;

[0036]FIG. 7 shows a relay method of a terminal when relay link
establishment is unavailable according to another exemplary embodiment of
the present invention;

[0037]FIG. 8 shows an example of path establishment through carrier
change in case of backhaul damage according to another exemplary
embodiment of the present invention; and

[0038]FIG. 9 shows an example of path establishment through frequency
change in case of backhaul damage according to another exemplary
embodiment of the present invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0039] In the following detailed description, only certain exemplary
embodiments of the present invention have been shown and described,
simply by way of illustration. As those skilled in the art would realize,
the described embodiments may be modified in various different ways, all
without departing from the spirit or scope of the present invention.
Accordingly, the drawings and description are to be regarded as
illustrative in nature and not restrictive. Like reference numerals
designate like elements throughout the specification.

[0040] In the overall specification, a mobile station (MS) may refer to a
terminal, a mobile terminal (MT), a subscriber station (SS), a portable
subscriber station (PSS), an access terminal (AT), user equipment (UE),
an advanced mobile station (AMS), a high reliability mobile station
(HR-MS), etc., and may include all or some of functions of the terminal,
MT, SS, PSS, AT, UE, AMS, HR-MS, etc.

[0041] A base station (BS) may refer to a node B, an evolved node B
(eNodeB), an access point (AP), a radio access station (RAS), a base
transceiver station, (BTS), a mobile multihop relay (MMR)-BS, an advanced
base station (ABS), a high reliability base station (HR-BS), a relay
station (RS) or an advanced relay station (ARS) that functions as a base
station, a high reliability relay station (HR-RS) that functions as a
base station, etc., and may include all or some of functions of the node
B, eNodeB, AP, RAS, BTS, MMR-BS, ABS, HR-BS, RS, ARS, HR-RS, etc.

[0042] A relay method of a base station will be described in detail with
reference to the attached drawings.

[0043] FIG. 1 shows a communication state according to an exemplary
embodiment of the present invention, FIG. 2 shows an example of relay
link establishment by a base station in case of backhaul damage according
to an exemplary embodiment of the present invention, and FIG. 3 shows an
example of handover performed by a terminal in case of backhaul damage
according to another exemplary embodiment of the present invention.

[0044] Referring to FIG. 1, a general communication system includes a
server 400 that manages base stations 110 and 120, and a terminal 200
that transmits/receives data to/from the base station 110. A backhaul
link is connected between the base stations 110 and 120 as well as among
the base stations 110, 120 and the server 400. The terminal 200 and the
base station 110 are connected to each other wirelessly. The terminal 200
can be provided with a wireless service or may report data through the
base station 110. The base station 110 can transmit data reported by the
terminal 200 to the server 400 or another communication apparatus through
a predefined path 10.

[0045] If the backhaul link of the base station 110 is destroyed, as shown
in FIG. 2, the base station 110 can function as a relay station by
establishing a relay link between the base station 110 and the base
station 120. Then, a path 20 including the base station 120 is
reestablished between the terminal 200 and the server 400, and thus the
service can be continuously provided between the terminal 200 and the
server 400.

[0046] Here, the terminal 200 is not provided with the service from the
server 400 until the mode of the base station 110 is changed to a relay
station, that is, until the relay link is established between the base
station 110 and the base station 120,

[0047] Even after the establishment of the relay link between the base
station 110 and the base station 120, delay may be generated on the path
between the base station 110 and the server 400 due to path
reestablishment between the base station 120 and the server 400. To
prevent this delay, it is necessary to share the path 10 that does not
include the base station 120 and the path 20 that includes the base
station 120 through the backhaul link between the base station 110 and
the base station 120 for the path between the base station 110 and the
server 400 in the general communication state, as shown in FIG. 1. Then,
the base station 120 can rapidly reestablish the path in the situation as
shown in FIG. 2.

[0048] To achieve this, the base station 110 transmits information to the
base station 120, as shown in FIG. 1 (S510). The information corresponds
to information about the terminal 200 to/from which the base station 110
transmits/receives data, and may include context information including
server information for data transmission/reception, a context ID, data
information at the time of backhaul link cutoff, and information about
data to be resumed. The information is periodically transmitted when the
backhaul link is unavailable or right before the backhaul link is
unavailable. Accordingly, when the path between the base station 110 and
the server 400 is unavailable, the path between the base station 120 and
the server 400 can minimize delay using the path 20 between the base
station 120 and the server 400, which is previously set up and managed,
if the relay link is set up between the base station 110 and the base
station 120.

[0049]FIG. 3 shows an exemplary communication state in which the terminal
200 performs a handover to the base station 120 due to unavailability of
the backhaul link of the base station 110 so as to resume
transmission/reception of data to/from the server 400. When the base
station 110 establishes the relay link between the base station 110 and
the base station 120, the base station 110 can transmit information to
the base station 120 (S510). In this case, the information includes the
ID of the terminal 200, a data context ID, and context information at the
time of data transmission/reception interruption and resumption. The
terminal 200 performs handover to the base station 120, and the base
station 120 can reestablish a path 30 on the basis of the previously set
path 20 or information received from the base station 110. Alternatively,
the terminal 200 can transmit context information to the base station 120
during the handover procedure (S520), and the base station 120 can
reestablish the path on the basis of the previously set path or the
received information.

[0050] In order for the terminal 200 to efficiently change the path
through the base station 110 to the path through the base station 120,
the base station 110 can inform the terminal 200 that the base station
110 and the base station 120 share the context information of the
terminal 200 even when the backhaul link is not unavailable (S530). In
this case, the base station 110 can inform the terminal 200 of a list of
neighbor base stations that share the context information of the terminal
200 and transmit information on priority of the neighbor base stations.
Accordingly, when the terminal 200 attempts to select a new path, the
terminal 200 can select a neighbor base station on the basis of the
received list or priority and handover to the selected neighbor base
station. The base station 110 and the base station 120 can share the
context information of the terminal 200 even after a relay link is
established after the backhaul link is unavailable.

[0051] That is, a base station or a relay station for which a relay link
is set up can establish a path for performing a handover on conditions
different from conditions of general base stations or relay stations
after the relay link is established. For example, if the neighbor base
station 120 has better channel quality than that of the current base
station 110, the terminal performs handover to the neighbor base station
120, in general. However, the communication system according to an
exemplary embodiment of the present invention can allow a handover to a
neighbor base station only when the neighbor base station has channel
quality that exceeds a predetermined standard even if the channel quality
of the neighbor base station is better than the current base station 110.

[0052] Furthermore, the base station or relay station for which the relay
link is established does not permit a terminal to enter the base station
or relay station (for example, using a cell bar bit in IEEE 802.16m
communication system), and when services are not smoothly provided due to
interference of a specific terminal, allows the terminal to enter the
base station or relay station such that connection between the terminal
and a previous base station or relay station can be cut off.

[0053] Moreover, in a communication in which a corresponding base station
or relay station can operate in multiple modes, distinguished from the
general base stations or relay stations, a base station or relay station
having a damaged backhaul link or a terminal capable of operating in
multiple modes can be restricted from entering a corresponding cell. To
achieve this, the above-mentioned other conditions can be given, or a
lower terminal can be informed of the fact that the corresponding cell is
a cell having a damaged backhaul link or serviced by a multi-mode
terminal. In this case, a specific preamble can be used, or information
shown in the following Table 1, 2, or 3 can be included in SFH in an IEEE
802.16m system or in a downlink channel descriptor (DCD) or system
configuration descriptor (SCD) in IEEE 802.16-2009.

[0054] Table 1 shows an exemplary indication of whether the current base
station or relay station is a base station or relay station operating in
a multi-mode environment or degraded network, which is included in an SCD
or DCD message.

[0055] In Table 1, the field is a 1-bit HR multi-mode indication, and
indicates whether the current base station or relay station is a terminal
acting as a base station or relay station or a base station acting as a
relay station.

[0056] Table 2 shows another exemplary indication of whether the current
base station or relay station is a base station or relay station
operating in a multi-mode environment or degraded network, which is
included in an SCD or DCD message.

[0057] Table 3 shows another exemplary indication of whether the current
base station or relay station is a base station or relay station
operating in a multi-mode environment or degraded network, which is
included in an SCD or DCD message.

[0058] Alternatively, when path setup or handover is performed for a
corresponding base station or a neighbor base station, information
indicating whether the neighbor base station is a normal base station or
relay station to which a backhaul link is connected or a base station or
relay station acting in multiple modes or having a relay link established
therefore can be included in a neighbor advertisement (NBR-ADV) message
and transmitted to a corresponding terminal such that the terminal can
perform a handover in consideration of the information.

[0059] A method for establishing an optimized path in a multi-mode
environment will be described in detail with reference to FIG. 4.

[0060]FIG. 4 illustrates an example of path reestablishment according to
another exemplary embodiment of the present invention, which shows a case
in which a relay link is set up between the current base station 110 and
the neighbor base station 120 because the backhaul link is unavailable
and thus the neighbor base station 120 provides a service. There is a
case in which a neighbor base station or relay station is a multi-mode
terminal that functions as the base station or relay station.

[0061] The current base station 110 can include information about a base
station, a relay station, or a multi-mode terminal, which operate in the
above-mentioned environment, in an NBR-ADV message, and transmit the
NBR-ADV message including the information. That is, the current base
station 110 can include the information as shown in Table 1, 2, or 3, or
information which represents that the base station or relay station is a
base station or relay station acting in multiple modes or degraded
network, in the NBR-ADV, and transmits the NBR-ADV.

[0062] In general, to perform a handover to a neighbor base station or
relay station, a terminal needs to periodically or aperiodically scan the
channel state of the neighbor base station. In this case, the terminal
reports the scanned channel state of the neighbor base station to a base
station or relay station to which the terminal is currently connected.
According to an exemplary embodiment of the present invention, it is
possible to differently define conditions in which information is
reported in consideration of the special situation of the degraded
network for the base station, relay station, and multi-mode terminal, as
shown in Table 1, 2, or 3, and inform the neighbor base station of the
conditions. The conditions can be included in an NBR-ADV message or SCD
or DCD message information. The base station notified of the conditions
recognizes that the corresponding base station or relay station is a base
station or relay station to which the current terminal can handover, and
transmits information about the terminal to the base station or relay
station through a relay link such that the terminal can perform a
handover rapidly and efficiently.

[0063] Table 4 shows an exemplary indication of whether a neighbor base
station or relay station is a base station or relay station acting in a
multi-mode environment or a degraded network, which is included in an
NBR-ADV message.

[0064] Table 5 shows another exemplary indication of whether a neighbor
base station or relay station is a base station or relay station acting
in a multi-mode environment or a degraded network, which is included in
an NBR-ADV message.

[0065] Table 6 shows another exemplary indication of whether a neighbor
base station or relay station is a base station or relay station acting
in a multi-mode environment or a degraded network, which is included in
an NBR-ADV message.

[0066] If base stations do not share the information about the terminal
when the terminal performs handover, the current base station transmits
the information about the terminal to an apparatus to which the terminal
can perform handover, such as a base station or relay station, such that
the terminal can perform handover to the apparatus. In this case, the
current base station can transmit a handover message including the
information as shown in Table 4 to the base station, relay station, or
multi-mode terminal requested by the terminal for a handover such that
the requested base station, relay station, or multi-mode terminal shares
the information about the terminal so as to resume the handover after a
predetermined time. The information about the terminal can be transmitted
to the neighbor base station through the backhaul link if the neighbor
base station is connected to the backhaul link. In a multi-mode
environment, however, the information about the terminal is transmitted
through a relay link connected between apparatuses since a network is
constructed through a radio link between the apparatuses. An AAI-L2-XFER
message used to transmit control information of an upper layer can be
employed to deliver the information about the terminal.

[0067] Table 7 shows a handover message (AAI-HO-CMD).

TABLE-US-00007
TABLE 7
Size
Field (bits) Value/Description Condition
Mode 2 0b00: HO command; N/A
0b01: Zone switch command
from MZone to LZone;
0b10: AMS HO request rejected (ABS in
list unavailable). In this case,
AAI-HO-CMD message shall not include
any T-ABS. However, if the requested
ABSs in list is available but MAC
information is not shared, those ABSs
may be included candidate T-ABS and
serving ABS transfers MS information via
backbone network or relay link.
0b11: Reserved
If (Mode ==
0b00) {
. . . . . . . . . . . .
}else if (Mode
== 0b01) {
. . . . . . . . . . . .
}else if
(Mode==0b10)
{
REQ-Duration 8 The 8 least significant bits of the absolute
superframe number where the AMS may
perform handover again (i.e., allowing
the AMS to transmit AAI-HO-REQ after
REQ-Duration).
for (i=0; i < N_Target_BS is the number of T-ABSs
N_Target_BS; or target legacy BSs included in this
i++) { message.
targetBSID 48 BSID of the T-ABS or target legacy BS. Shall be included
SA-Preamble 10 Indicates the SA-Preamble index of the Shall be included if
Index carrier. the BS is T-ABS
Preamble Index 7 Indicates the preamble index of the Shall be included if
neighbor BS. the BS is target
legacy BS
Center 32 Indicates center frequency (in unit of Hz) Shall be included
Frequency of the carrier.
}
}

[0068] A method for establishing an optimized path in a multi-mode
environment according to another exemplary embodiment will be described
in detail with reference to FIGS. 5 and 6.

[0069]FIG. 5 shows an example of path reestablishment according to
another exemplary embodiment of the present invention, and FIG. 6 shows
another example of path reestablishment according to another exemplary
embodiment of the present invention.

[0070] Referring to FIG. 5, the base station 110 and the base station 120
share the information about the terminal 200 and the terminal 200
transmits/receives data through the base station 110. FIG. 6 shows a case
in which the base station 110 and the base station 120 acting as a relay
station share the information about the terminal 200, and the terminal
200 transmits/receives data through the base station 110.

[0071] In the case of FIG. 5, the service is provided to the terminal 200
through the base station 110 while the base station 120 maintains
connection information, and the path between the base station 110 and the
terminal 200 corresponds to an active path. Accordingly, data can be
transmitted through the base station 120 that shares the information
about the terminal 200 without an additional operation when the service
cannot be provided through the base station 110, or as necessary.

[0072] However, when the base station 110 establishes a relay link with
the base station 120 due to cutoff of the backhaul link to provide the
service to the terminal 200, as shown in FIG. 6, provision of the service
to the terminal 200 by the base station 110 may be restricted compared to
the case of FIG. 5. In this case, the service can be provided to the
terminal 200 through the base station 120 because the base station 110
and the base station 120 share the information about the terminal 200 as
described above. That is, the path connected between the base station 110
and the terminal 200 corresponds to an active path, and the path
connected between the base station 120 and the terminal 200 is designated
as an alternative path or backup path and managed in the case of FIG. 5,
whereas the path connected between the base station 110 and the terminal
200 is changed to an alternative path or backup path and the path
connected between the base station 120 and the terminal 200 is changed to
an active path to continuously provide the service in the case of FIG. 6.
However, path reestablishment can be performed even in the case of FIG. 5
irrespective of the cause of path reestablishment such as backhaul link
damage.

[0073] The above-mentioned multi-path establishment method can also be
applied to a case of recovery of the destroyed backhaul link. While one
alternative path or backup back is illustrated in FIGS. 5 and 6, one or
more alternative paths or backup paths can be available, and a path
selected from the one or more alternative paths or backup paths can
become an active path and a previous active path can be changed to an
alternative path or backup path. That is, a most reliable path from among
a plurality of alternative paths or backup paths can be set as an active
path, and reliability can be determined based on various conditions. For
example, the reliability can be determined in consideration of a load of
an upper apparatus that provides a service to the terminal in addition to
presence or absence of the backhaul link.

[0074] The above description can be applied to a base station operating in
multiple modes. Furthermore, the present embodiment can be applied to a
case in which a relay station instead of the terminal 200 communicates
with an upper base station or upper relay station through a relay link.

[0075] A case in which a relay link cannot be set up between base stations
will be described in detail with reference to FIG. 7.

[0076]FIG. 7 shows a relay method of a terminal when a relay link cannot
be set up according to another exemplary embodiment of the present
invention.

[0077] As shown in FIG. 7, the terminal 200 can relay data between the
base station 110 and the base station 120 when the base station 110 and
the base station 120 have difficulty in setting up or a relay link cannot
be established. In this case, a connection path between an upper base
station, that is, the base station 110 or the base station 120 and the
terminal 200 is present, and thus the service can be provided through the
connection path. Here, an alternative path or backup path and an active
path can be periodically changed. The terminal 200 can function as a
relay station to provide the service to a lower terminal or simply
perform the function of the terminal to relay data between the base
station 110 and the base station 120.

[0078] The above description can be applied when the base stations 110 and
120 operate in multiple modes. The present embodiment can be applied to a
case in which a relay station instead of the terminal 200 communicates
with a base station or relay station through a relay link.

[0079] While FIG. 7 shows the base stations 110 and 120, the base stations
110 and 120 can be replaced by two neighbor relay stations in all the
figures and description of the specification.

[0080] A multi-path establishment method of a base station in a
multi-carrier environment will be described in detail with reference to
FIG. 8.

[0081]FIG. 8 shows an example of path establishment through carrier
change in case of backhaul damage according to another exemplary
embodiment of the present invention.

[0082] Referring to FIG. 8, one carrier operates as a primary carrier and
the other carriers operate as secondary carriers according to capability
of the terminal 200 when the base station 110 and the terminal 200
communicate with each other using multiple carriers. If a specific
carrier is unavailable or service quality is deteriorated, the terminal
200 needs to change the currently serviced carrier to a carrier having
better service quality than the currently serviced carrier.

[0083] To achieve this, the base station 110 transmits state information
of the carrier to the terminal 200 when estimating that the carrier is
unavailable or service quality is deteriorated (S540). The state
information may include the cause of service quality deterioration, cause
of unavailability, service resumption estimation time, or unavailable
time. For this, the base station 110 needs to store serviced path
information of the terminal 200 in the base station 110 and manage the
information.

[0084] Upon reception of the state information of the carrier, the
terminal 200 can recognize the state of the carrier and change the
serviced carrier. To efficiently perform this operation, the terminal 200
can periodically measure a channel state by scanning states of carriers
other than the currently serviced carrier. In addition, the terminal 200
can change the currently serviced carrier to a carrier with better
quality through the measured channel state.

[0085] A multi-path establishment method of a base station in a multi-path
environment will be described in detail with reference to FIG. 9.

[0086]FIG. 9 shows an example of path establishment through frequency
change in case of backhaul damage according to another exemplary
embodiment of the present invention.

[0087]FIG. 9 shows a case in which the base station 110 sets up an
optimized path from among multiple paths through frequency change, that
is, inter-frequency handover (inter-FA HO), when the base station 110
provides the service using multiple frequencies. As shown in FIG. 8, when
a specific frequency cannot provide a service or service quality is
deteriorated, the base station 110 transmits information about this state
to the terminal 200 (S550). This state information may include the cause
of quality deterioration, cause of unavailability, service resumption
estimation time, or unavailable time.

[0088] Then, the terminal 200 changes the frequency, that is, performs
inter-frequency handover, as in the case of FIG. 8. While the
inter-frequency handover can be performed at the request of the base
station 110, the terminal 200 may perform the inter-frequency handover by
measuring the channel state for each frequency. Here, the base station
110 stores and manages service path information of the terminal 200
irrespective of frequency so as to achieve efficient and optimized path
change.

[0089] When a base station or relay station cannot perform the function
thereof in a communication system since a backhaul link of the base
station is damaged, a path through which a communication service is
continuously provided through a neighbor base station or relay station
can be established without delay.

[0090] Furthermore, when a base station that provides a service using
multiple carriers or multiple frequencies does not satisfy carrier or
frequency service, the base station can continue providing the service
using other carriers or frequencies.

[0091] While this invention has been described in connection with what is
presently considered to be practical exemplary embodiments, it is to be
understood that the invention is not limited to the disclosed
embodiments, but, on the contrary, is intended to cover various
modifications and equivalent arrangements included within the spirit and
scope of the appended claims.

Patent applications by Chul Sik Yoon, Daejeon KR

Patent applications by Eunkyung Kim, Daejeon KR

Patent applications by Hyun Lee, Daejeon KR

Patent applications by Kwang Jae Lim, Daejeon KR

Patent applications by Mi-Young Yun, Daejeon KR

Patent applications by Sung Cheol Chang, Daejeon KR

Patent applications by Sung Kyung Kim, Daejeon KR

Patent applications by Won-Ik Kim, Daejeon KR

Patent applications by Electronics and Telecommunications Research Institute